A typical rotary vane actuator has a housing providing a fixed volume cavity (an enclosed space). The cavity is divided into first and second chambers by a vane assembly. The vane assembly is rotatable within the cavity about a vane axle provided adjacent to an end of the vane assembly.
Pressurised fluid is separately provided to each of the first and second chambers by respective ports. In order to generate rotation of the vane assembly in a direction from the first chamber to the second chamber, the pressure of the pressurised fluid in the first chamber is increased by introducing additional pressurised fluid into the first chamber, and/or the pressure in the second chamber is reduced by removing some pressurised fluid from the second chamber. A pressure difference is therefore generated across the vane assembly between a higher pressure in the first chamber and a lower pressure in the second chamber. This pressure difference generates a torque on the vane assembly, resulting in rotational movement of the vane assembly in a direction away from the first chamber towards the second chamber.
As the vane assembly rotates, additional pressurised fluid continues to be introduced into the first chamber, and/or pressurised fluid continues to be removed from the second chamber, to maintain the pressure difference between the first and second chambers.
Rotation of the vane assembly in an opposite direction away from the second chamber towards the first chamber is achieved in an equivalent manner by providing a higher pressure in the second chamber than in the first chamber, by introducing additional pressurised fluid to the second chamber and/or by removing pressurised fluid from the first chamber.
Typically, a stop is provided in the housing to fix an extreme of a range of rotational motion of the vane assembly. For example, it is known to provide a bolt or screw that protrudes into the housing so that the vane assembly contacts a tip of the bolt or screw when the vane assembly is at an extreme rotational position, so that the vane assembly is prevented from rotating beyond that position. In practice, two such stops are normally provided, one in the first chamber and one in the second chamber, to delimit two extremes of the range of rotational motion of the vane assembly. The stop is typically adjustable, but this is not essential. For example, typically the stop is a threaded bolt or screw that extends into the cavity through a threaded hole in the housing, so that an extent to which a tip of the bolt or screw protrudes into the housing can be adjusted by rotating the bolt or screw relative to the housing.
Energy is fed into the actuator by the flow of pressurised fluid and converted into mechanical work in the form of rotation of the vane axle against a torque imposed on the vane axle by an external load.
The construction of the vane assembly is important to the efficiency of the actuator. In particular, it is important that the vane assembly provides a seal between the first and second chambers so that the energy from the input flow of pressurised fluid is efficiently converted into rotational work, rather than being wasted by leaking between the first and second chambers around the vane assembly.
The vane assembly must also be able to withstand loads applied to the vane assembly by the pressurised fluid, and loads applied to the vane assembly when the vane assembly contacts a stop and is pressed against the stop.
Different constructions for the vane assembly are known. A known construction will now be discussed with reference to FIGS. 1 to 4. FIG. 1 is an exploded view of a known vane assembly 1, FIG. 2(a) is a side view of the known vane assembly 1, FIG. 2(b) is a cross-sectional view along the line A-A of FIG. 2(a) showing the internal structure of the known vane assembly 1, FIG. 3 is an exploded view of a rotary vane actuator including the known vane assembly 1, and FIG. 4 is a cross-sectional view of a rotary vane actuator including the known vane assembly 1.
As shown in FIG. 1, the known vane assembly 1 comprises a vane 3 that has a shaft 5 provided adjacent to an end of the vane 3, so that the vane 3 and shaft 5 are rotatable together about a central axis of the shaft 5. The vane 3 is generally in the form of a rigid paddle, and is made of rigid material, typically steel.
A first vane seal 7 is provided on a first surface of the vane 3. The first vane seal 7 is made of a flexible material such as polyurethane. The first vane seal 7 has a seal lip 9 around the outer periphery thereof. When the known vane assembly 1 is positioned in an appropriate housing (discussed below with reference to FIGS. 3 and 4), so that the vane assembly 1 separates the housing into first and second chambers, the seal lip 9 of the first vane seal 7 contacts an inner surface of the housing to form a seal between the vane assembly 1 and the housing that prevents, or substantially prevents, the leaking of pressurised fluid from the first chamber to the second chamber.
A first seal expander 11, made from a springy material such as steel, is also provided. The first seal expander 11 is shaped to contact and apply force to an inner surface of the seal lip 9 of the seal 7, to keep the seal lip 9 in contact with an inner surface of the housing so as to maintain a good seal. The first seal expander 11 overcomes a problem of creep under stress of the seal material which may otherwise occur. However, the first seal expander 11 is not essential. For example, the first seal expander 11 can be omitted where the first vane seal 7 is made of a creep resistant material.
The first vane seal 7 and first seal expander 11 are clamped in position on the first side of the vane 3 by a first side-plate 13.
The first side-plate 13 is made of plastic, and is manufactured by a suitable moulding or casting process, such as injection moulding. The first side-plate 13 is substantially hollow and has an internal void 15. The internal void 15 is exposed on an inner surface of the first side-plate 13, so that the internal void 15 is accessible from the inner surface of the first side-plate 13.
In an alternative known construction the first side-plate 13 is instead formed from sheet metal which is cut to the required shape and formed by bending the cut sheet into the desired profile for the first side-plate. However, this alternative known construction is typically more wasteful in terms of compressed fluid usage during operation of the rotary vane actuator.
The first side-plate 13 has sufficient strength to withstand pressures applied to the first side-plate 13 by pressurised fluid when the known vane assembly 1 is used in a rotary vane actuator, and to withstand pressures applied to the first side-plate 13 when the first side-plate 13 contacts and is pressed against a stop in a cavity of a housing of the rotary vane actuator. To increase the strength of the first side-plate 15, strengthening ribs are provided in the internal void 15 of the first side-plate 13.
The first side-plate 13 is moulded to a have a shape for taking up more volume of a cavity of a housing of a rotary vane actuator than a simple flat metal side-plate. Specifically, as shown in FIGS. 1 to 3, the first side-plate includes a protruding curved portion, or bulbous portion, 14 proximal to the position of the shaft 5. In the curved, or bulbous, portion 14 an outer surface of the first side-plate 13 is curved outwards, so that the overall volume of the first side-plate 13 is increased relative to a simple flat metal side-plate. In particular, the curved, or bulbous, portion 14 occupies space when the vane assembly is at an extreme of its range of rotational motion that would otherwise be dead/empty space.
Thus, the volume of the cavity in the housing occupied by the vane assembly 1 is increased relative to a simple flat metal side-plate. This has an advantage of reducing a volume of pressurised fluid that needs to be supplied to the first or second chamber of the cavity to cause rotational movement of the vane assembly 1, because the empty volume of the cavity is reduced.
A corresponding arrangement of a second vane seal 17, second seal expander 19 and second side-plate 21 is provided on an opposite second side of the vane 3. The arrangement on the second side of the vane 3 is a mirror image of the arrangement on the first side of the vane 3, and the descriptions given above of the first vane seal 7, first seal expander 11 and first side-plate 21 also apply to the corresponding second vane seal 17, second seal expander 19 and second side-plate 21.
The vane assembly 1 is held together using threaded screws 23 and corresponding nuts 25, so that the vane seals 7, 17 and seal expanders 11, 19 are sandwiched between the side-plates 13, 21 and the vane 3 and clamped in position. Specifically, the threaded screws 23 extend through the vane assembly 1 from one side of the vane assembly 1 to the other side through corresponding holes formed in the side-plates 13, 21, seal expanders 11, 19, vane seals 7, 17 and vane 3, and the corresponding nuts 25 are connected to the ends of the threaded screws 23 and tightened so that the side-plates 13, 21 clamp the vane seals 7, 17 and seal expanders 11, 19 in position against the vane 3. Alternatively, it is also known to use a combination of studs or bolts and nuts to hold the vane assembly 1 together.
FIG. 3 shows an exploded view of a known rotary vane actuator 27 including the known vane assembly 1. As shown in FIG. 3, the rotary vane actuator 27 has a housing comprising a first shell part 29 and a second shell part 31. When the first shell part 29 and second shell part 31 are joined together, an enclosed cavity 33 is formed between them.
As shown in FIG. 3, the vane assembly 1 is positioned in the enclosed cavity 33 between the first and second shell parts 29, 31. The second shell part 31 has an opening 35 at an upper part thereof for receiving the shaft 5 of the vane assembly 1, so that the vane assembly 1 is rotatably mounted in the cavity 33.
The vane assembly 1 therefore separates the cavity 33 into first and second chambers, and the vane seals 7, 17 form a pneumatic seal between the first and second chambers that prevents, or substantially prevents, fluid from passing between the first and second chambers around the vane assembly 1.
As shown in FIG. 3, at least one stop 34, in the form of a threaded screw that extends through the housing into the cavity 33, is provided to set an extreme of the rotation of the vane assembly within the cavity 33. In practice, two such stops may be provided, one on each side of the cavity 33 to set two opposite extremes of the rotation of the vane assembly. Typically the stops will be adjustable, so that an extent to which the stop extends into the cavity can be adjusted, for example by rotating the stop, e.g. where the stop is a threaded screw.
FIG. 4 is a schematic illustration of the known vane assembly 1 separating a cavity of a housing 36 of a rotary vane actuator into first and second chambers 37 and 38, as discussed above.